Commit 622838f3 authored by Al Viro's avatar Al Viro
Browse files

iov_iter: make the amount already copied available to iterator callbacks 



Making iterator macros keep track of the amount of data copied is pretty
easy and it has several benefits:
	1) we no longer need the mess like (from += v.iov_len) - v.iov_len
in the callbacks - initial value + total amount copied so far would do
just fine.
	2) less obviously, we no longer need to remember the initial amount
of data we wanted to copy; the loops in iterator macros are along the lines
of
	wanted = bytes;
	while (bytes) {
		copy some
		bytes -= copied
		if short copy
			break
	}
	bytes = wanted - bytes;
Replacement is
	offs = 0;
	while (bytes) {
		copy some
		offs += copied
		bytes -= copied
		if short copy
			break
	}
	bytes = offs;
That wouldn't be a win per se, but unlike the initial value of bytes, the amount
copied so far *is* useful in callbacks.
	3) in some cases (csum_and_copy_..._iter()) we already had offs manually
maintained by the callbacks.  With that change we can drop that.

	Less boilerplate and more readable code...

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 21b56c84

lib/iov_iter.c

+50 −70
Original line number Diff line number Diff line
@@ -17,15 +17,14 @@ 
#define PIPE_PARANOIA /* for now */



/* covers iovec and kvec alike */

#define iterate_iovec(i, n, __v, __p, skip, STEP) {		\

	size_t left;						\

	size_t wanted = n;					\

#define iterate_iovec(i, n, __v, __off, __p, skip, STEP) {	\

	size_t __off = 0;					\

	do {							\

		__v.iov_len = min(n, __p->iov_len - skip);	\

		if (likely(__v.iov_len)) {			\

			__v.iov_base = __p->iov_base + skip;	\

			left = (STEP);				\

			__v.iov_len -= left;			\

			__v.iov_len -= (STEP);			\

			__off += __v.iov_len;			\

			skip += __v.iov_len;			\

			n -= __v.iov_len;			\

			if (skip < __p->iov_len)		\
@@ -34,11 +33,11 @@ 
		__p++;						\

		skip = 0;					\

	} while (n);						\

	n = wanted - n;						\

	n = __off;						\

}



#define iterate_bvec(i, n, __v, p, skip, STEP) {		\

	size_t wanted = n;					\

#define iterate_bvec(i, n, __v, __off, p, skip, STEP) {		\

	size_t __off = 0;					\

	while (n) {						\

		unsigned offset = p->bv_offset + skip;		\

		unsigned left;					\
@@ -50,6 +49,7 @@ 
		left = (STEP);					\

		kunmap_local(kaddr);				\

		__v.iov_len -= left;				\

		__off += __v.iov_len;				\

		skip += __v.iov_len;				\

		if (skip == p->bv_len) {			\

			skip = 0;				\
@@ -59,13 +59,14 @@ 
		if (left)					\

			break;					\

	}							\

	n = wanted - n;						\

	n = __off;						\

}



#define iterate_xarray(i, n, __v, skip, STEP) {		\

#define iterate_xarray(i, n, __v, __off, skip, STEP) {		\

	__label__ __out;					\

	size_t __off = 0;					\

	struct page *head = NULL;				\

	size_t wanted = n, seg, offset;				\

	size_t seg, offset;					\

	loff_t start = i->xarray_start + skip;			\

	pgoff_t index = start >> PAGE_SHIFT;			\

	int j;							\
@@ -84,25 +85,26 @@ 
		for (j = (head->index < index) ? index - head->index : 0; \

		     j < thp_nr_pages(head); j++) {			\

			void *kaddr = kmap_local_page(head + j);	\

			offset = (i->xarray_start + skip) % PAGE_SIZE;	\

			offset = (start + __off) % PAGE_SIZE;		\

			__v.iov_base = kaddr + offset;			\

			seg = PAGE_SIZE - offset;			\

			__v.iov_len = min(n, seg);			\

			left = (STEP);					\

			kunmap_local(kaddr);				\

			__v.iov_len -= left;				\

			__off += __v.iov_len;				\

			n -= __v.iov_len;				\

			skip += __v.iov_len;				\

			if (left || n == 0)				\

				goto __out;				\

		}							\

	}							\

__out:								\

	rcu_read_unlock();					\

	n = wanted - n;						\

	skip += __off;						\

	n = __off;						\

}



#define __iterate_and_advance(i, n, v, I, K) {			\

#define __iterate_and_advance(i, n, v, off, I, K) {		\

	if (unlikely(i->count < n))				\

		n = i->count;					\

	if (likely(n)) {					\
@@ -110,31 +112,31 @@ __out: \ 
		if (likely(iter_is_iovec(i))) {			\

			const struct iovec *iov = i->iov;	\

			struct iovec v;				\

			iterate_iovec(i, n, v, iov, skip, (I))	\

			iterate_iovec(i, n, v, off, iov, skip, (I))	\

			i->nr_segs -= iov - i->iov;		\

			i->iov = iov;				\

		} else if (iov_iter_is_bvec(i)) {		\

			const struct bio_vec *bvec = i->bvec;	\

			struct kvec v;				\

			iterate_bvec(i, n, v, bvec, skip, (K))	\

			iterate_bvec(i, n, v, off, bvec, skip, (K))	\

			i->nr_segs -= bvec - i->bvec;		\

			i->bvec = bvec;				\

		} else if (iov_iter_is_kvec(i)) {		\

			const struct kvec *kvec = i->kvec;	\

			struct kvec v;				\

			iterate_iovec(i, n, v, kvec, skip, (K))	\

			iterate_iovec(i, n, v, off, kvec, skip, (K))	\

			i->nr_segs -= kvec - i->kvec;		\

			i->kvec = kvec;				\

		} else if (iov_iter_is_xarray(i)) {		\

			struct kvec v;				\

			iterate_xarray(i, n, v, skip, (K))	\

			iterate_xarray(i, n, v, off, skip, (K))	\

		}						\

		i->count -= n;					\

		i->iov_offset = skip;				\

	}							\

}

#define iterate_and_advance(i, n, v, I, K) \

	__iterate_and_advance(i, n, v, I, ((void)(K),0))

#define iterate_and_advance(i, n, v, off, I, K) \

	__iterate_and_advance(i, n, v, off, I, ((void)(K),0))



static int copyout(void __user *to, const void *from, size_t n)

{
@@ -607,14 +609,13 @@ static size_t csum_and_copy_to_pipe_iter(const void *addr, size_t bytes, 


size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)

{

	const char *from = addr;

	if (unlikely(iov_iter_is_pipe(i)))

		return copy_pipe_to_iter(addr, bytes, i);

	if (iter_is_iovec(i))

		might_fault();

	iterate_and_advance(i, bytes, v,

		copyout(v.iov_base, (from += v.iov_len) - v.iov_len, v.iov_len),

		memcpy(v.iov_base, (from += v.iov_len) - v.iov_len, v.iov_len)

	iterate_and_advance(i, bytes, v, off,

		copyout(v.iov_base, addr + off, v.iov_len),

		memcpy(v.iov_base, addr + off, v.iov_len)

	)



	return bytes;
@@ -703,17 +704,13 @@ static size_t copy_mc_pipe_to_iter(const void *addr, size_t bytes, 
 */

size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i)

{

	const char *from = addr;



	if (unlikely(iov_iter_is_pipe(i)))

		return copy_mc_pipe_to_iter(addr, bytes, i);

	if (iter_is_iovec(i))

		might_fault();

	__iterate_and_advance(i, bytes, v,

		copyout_mc(v.iov_base, (from += v.iov_len) - v.iov_len,

			   v.iov_len),

		copy_mc_to_kernel(v.iov_base, (from += v.iov_len)

					- v.iov_len, v.iov_len)

	__iterate_and_advance(i, bytes, v, off,

		copyout_mc(v.iov_base, addr + off, v.iov_len),

		copy_mc_to_kernel(v.iov_base, addr + off, v.iov_len)

	)



	return bytes;
@@ -723,16 +720,15 @@ EXPORT_SYMBOL_GPL(_copy_mc_to_iter); 


size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)

{

	char *to = addr;

	if (unlikely(iov_iter_is_pipe(i))) {

		WARN_ON(1);

		return 0;

	}

	if (iter_is_iovec(i))

		might_fault();

	iterate_and_advance(i, bytes, v,

		copyin((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len),

		memcpy((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)

	iterate_and_advance(i, bytes, v, off,

		copyin(addr + off, v.iov_base, v.iov_len),

		memcpy(addr + off, v.iov_base, v.iov_len)

	)



	return bytes;
@@ -741,15 +737,14 @@ EXPORT_SYMBOL(_copy_from_iter); 


size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i)

{

	char *to = addr;

	if (unlikely(iov_iter_is_pipe(i))) {

		WARN_ON(1);

		return 0;

	}

	iterate_and_advance(i, bytes, v,

		__copy_from_user_inatomic_nocache((to += v.iov_len) - v.iov_len,

	iterate_and_advance(i, bytes, v, off,

		__copy_from_user_inatomic_nocache(addr + off,

					 v.iov_base, v.iov_len),

		memcpy((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)

		memcpy(addr + off, v.iov_base, v.iov_len)

	)



	return bytes;
@@ -773,16 +768,13 @@ EXPORT_SYMBOL(_copy_from_iter_nocache); 
 */

size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i)

{

	char *to = addr;

	if (unlikely(iov_iter_is_pipe(i))) {

		WARN_ON(1);

		return 0;

	}

	iterate_and_advance(i, bytes, v,

		__copy_from_user_flushcache((to += v.iov_len) - v.iov_len,

					 v.iov_base, v.iov_len),

		memcpy_flushcache((to += v.iov_len) - v.iov_len, v.iov_base,

			v.iov_len)

	iterate_and_advance(i, bytes, v, off,

		__copy_from_user_flushcache(addr + off, v.iov_base, v.iov_len),

		memcpy_flushcache(addr + off, v.iov_base, v.iov_len)

	)



	return bytes;
@@ -911,7 +903,7 @@ size_t iov_iter_zero(size_t bytes, struct iov_iter *i) 
{

	if (unlikely(iov_iter_is_pipe(i)))

		return pipe_zero(bytes, i);

	iterate_and_advance(i, bytes, v,

	iterate_and_advance(i, bytes, v, count,

		clear_user(v.iov_base, v.iov_len),

		memset(v.iov_base, 0, v.iov_len)

	)
@@ -933,9 +925,9 @@ size_t copy_page_from_iter_atomic(struct page *page, unsigned offset, size_t byt 
		WARN_ON(1);

		return 0;

	}

	iterate_and_advance(i, bytes, v,

		copyin((p += v.iov_len) - v.iov_len, v.iov_base, v.iov_len),

		memcpy((p += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)

	iterate_and_advance(i, bytes, v, off,

		copyin(p + off, v.iov_base, v.iov_len),

		memcpy(p + off, v.iov_base, v.iov_len)

	)

	kunmap_atomic(kaddr);

	return bytes;
@@ -1656,28 +1648,22 @@ EXPORT_SYMBOL(iov_iter_get_pages_alloc); 
size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum,

			       struct iov_iter *i)

{

	char *to = addr;

	__wsum sum, next;

	size_t off = 0;

	sum = *csum;

	if (unlikely(iov_iter_is_pipe(i) || iov_iter_is_discard(i))) {

		WARN_ON(1);

		return 0;

	}

	iterate_and_advance(i, bytes, v, ({

	iterate_and_advance(i, bytes, v, off, ({

		next = csum_and_copy_from_user(v.iov_base,

					       (to += v.iov_len) - v.iov_len,

					       addr + off,

					       v.iov_len);

		if (next) {

		if (next)

			sum = csum_block_add(sum, next, off);

			off += v.iov_len;

		}

		next ? 0 : v.iov_len;

	}), ({

		sum = csum_and_memcpy((to += v.iov_len) - v.iov_len,

				      v.iov_base, v.iov_len,

		sum = csum_and_memcpy(addr + off, v.iov_base, v.iov_len,

				      sum, off);

		off += v.iov_len;

	})

	)

	*csum = sum;
@@ -1689,33 +1675,27 @@ size_t csum_and_copy_to_iter(const void *addr, size_t bytes, void *_csstate, 
			     struct iov_iter *i)

{

	struct csum_state *csstate = _csstate;

	const char *from = addr;

	__wsum sum, next;

	size_t off;



	if (unlikely(iov_iter_is_pipe(i)))

		return csum_and_copy_to_pipe_iter(addr, bytes, _csstate, i);



	sum = csum_shift(csstate->csum, csstate->off);

	off = 0;

	if (unlikely(iov_iter_is_discard(i))) {

		WARN_ON(1);	/* for now */

		return 0;

	}

	iterate_and_advance(i, bytes, v, ({

		next = csum_and_copy_to_user((from += v.iov_len) - v.iov_len,

	iterate_and_advance(i, bytes, v, off, ({

		next = csum_and_copy_to_user(addr + off,

					     v.iov_base,

					     v.iov_len);

		if (next) {

		if (next)

			sum = csum_block_add(sum, next, off);

			off += v.iov_len;

		}

		next ? 0 : v.iov_len;

	}), ({

		sum = csum_and_memcpy(v.iov_base,

				     (from += v.iov_len) - v.iov_len,

				     addr + off,

				     v.iov_len, sum, off);

		off += v.iov_len;

	})

	)

	csstate->csum = csum_shift(sum, csstate->off);